The prior art includes a variety of mechanisms which can be employed to effect relative pivotal movement between two structures. The design of such mechanisms varies in accordance with their application. In the aircraft industry, for example, the design requirements of these mechanisms are particularly stringent. Mechanisms for pivotally actuating and positioning flaps, trim devices, and other control surfaces must be capable of precisely controlled operation in the environment of complex counterforces. The in-flight loads opposing operation of aircraft control surfaces can be both severe and multidirectional. A variety of external loads must be resisted or overcome.
In addition to meeting severe structural requirements, mechanisms for actuating aircraft control surfaces are also subject to other design considerations. Reasonable standards of weight, size, power consumption, reliability, and operational precision must also be satisfied. It will be appreciated that the problems discussed so far with respect to the actuation of aircraft control surfaces are more pronounced in the case of variable camber airfoils or the like having two or more serially connected movable airfoil segments, each of which must be pivoted in a controlled manner with respect to adjacent segments.
A large part of the problem involves the fact that the length of the moment arm through which the control forces are applied is generally limited by the local thickness of the airfoil, since such actuator mechanisms are typically installed within the external profile of the airfoil to reduce drag. Since the length of a vertical moment arm is limited by the airfoil thickness, the associated gearing and drive transmission must be of greater capacity and therefore greater weight. On the other hand, while a horizontal moment arm can be of relatively greater length, its pivotal movement is also limited by the thickness of the airfoil. Once again, these difficulties become even more formidable with respect to variable camber airfoils or thin section airfoils.
In a departure from more traditional approaches, the prior art includes the teaching of a "bent beam" type mechanism in such applications. U.S. Pat. No. 3,944,170, of common inventorship and assignment herewith, teaches an apparatus for producing pivotal movement which employes a rotatable bent beam member. While the device disclosed and claimed therein operates satisfactorily, it has been found that the device can be further improved. It has been found that some of the objectives of my earlier invention can be accomplished with even more efficiency. It has been found that the same basic structure can be more efficiently driven by means of various other drive arrangements. For example, the use of an internal, integral actuator eliminates some of the typical problems associated with the gear driven transmissions of the prior art, such as weight, play, maintenance, size, expense and the like. With an integral actuator, power transmission losses are eliminated and large actuation forces can be developed in a compact envelope.
The present invention, in each of its embodiments, incorporates an indexing gear independent of the driving gear. In my prior patent, the embodiment illustrated incorporated a bevel drive gear external of the housing which itself served as an indexing gear for causing equal opposite rotational movement of the bent beam and the oppositely rotatable housing or carrier.
Accordingly, it is a primary object of the present invention to provide an improved eccentric actuator mechanism for effecting relative pivotal movement between first and second structures.
Another object is to provide an eccentric actuator apparatus capable of effecting precisely controlled, relative pivotal movement of two structures while bearing substantial loads between the structures.
Yet another object is to provide an eccentric actuator which incorporates an independent indexing means separate from the drive gear to permit utilization of various drive systems offering various advantages and efficiencies.
Another object is to provide a pivotal actuator for aircraft control surfaces compatible with airfoils of thin section and having the moment arm extending in a generally chordwise direction within the airfoil.
A further object is to provide an eccentric actuator inherently providing a substantial amount of mechanical reduction particularly at the extremes of pivotal range of the device.
A still further object is to provide an improved actuator which is particularly adapted for use in a vehicle steering system.